Optical wavelength switch having planar lightwave circuit structure

ABSTRACT

An optical wavelength switch having a planar wave-guide formed on a substrate including a wave-guide-type diffraction grating having an input/output wave-guide with an under-clad layer on a sacrificial layer formed on the substrate, a core layer formed on the under-clad layer and an over-clad layer formed on the core layer. The switch including a first slab wave-guide connected with the input/output wave-guide, an array wave-guide with one side connected to the first slab wave guide, a second slab wave-guide connected to the other side of the array wave-guide, and a movable girder secured to the substrate. The movable girder has the same under-clad layer, core layer and over-clad layer as the wave-guide-type diffraction grating. The switch has a minor at the tip of the movable girder, the mirror facing an end face of the second slab wave-guide, and the displaceable along a direction perpendicular to the optical axis.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 10/799,579filed Mar. 11, 2004, now U.S. Pat. No. 7,095,918, which claims priorityfrom Japanese Patent Application 2003-185190 filed Jun. 27, 2003, thecontents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical wavelength switch having aplanar lightwave circuit structure for use in optical communication,etc.

2. Description of the Related Arts

In recent years, communication capacity has explosively increased andconstruction of a photonic network having a large capacity usingWavelength Division Multiplexing (WDM) for coping with the increase hasmade progress. For an efficient composition of the WDM photonic network,wavelength switches are indispensable which realize Optic Add-DropModules (OAD) or optical cross-connect modules disposed in opticaltransmission paths.

FIG. 1 is a diagram illustrating an optical add-drop module 10 and thismodule 10 inputs an input optical beam having beenwavelength-multiplexed from a previous-stage node into an input port 11and inputs an insert (Add) optical beam having a specific wavelength atthe node into an insert port 12. Furthermore, a part of the inputoptical beam 11 and the insertion optical beam 12 are outputtedunprocessed passing through (Through) to an output-side port 13 and apart of the input optical beam 11 having a specific wavelength isbranched (Drop) to a branch port 14.

The functions of insertion (Add), passing through (Through) andbranching (Drop) of an optical signal at the optical add-drop module 10are realized by a wavelength switch. For a conventional wavelengthswitch having such functions, a composition as shown in FIG. 2 is known(see U.S. Pat. No. 5,960,133).

A composition shown in FIG. 2 comprises a combination of a diffractiongrating (spectral function) 101, a MEMS (Micro-Electro MechanicalSystem) mirror 102 having a switching function and a focus lens 103.

The input optical beam (IN) and the insertion optical beam (ADD) aredivided by the diffraction granting 101 into optical beams for eachwavelength and inputted into the MEMS mirror 102 through the focus lens103. At the MEMS mirror 102, it is possible to switch an optical beam toeither an output (OUT) port or a branch (DROP) port by controlling theangle of the mirror.

Here, in order to downsize a WDM transmission system and reduce the coston it, it is desired to realize the functions of the optical add-dropmodule 10 described referring to FIG. 1 using planar lightwave circuit(PLC) type functional integrated circuits capable of being mass-producedusing a batch process.

However, for a combination of a diffraction grating 101 and an MEMSmirror 102 having a composition of a conventional example shown in FIG.2, a high-precision alignment is necessary for the focus lens 103 andthe MEMS mirror 102 in order to focus optical beam emitted from thediffraction grating 101, on the MEMS mirror 102.

To this end, there are problems that the number of assembly stepsbecomes great many and that cost reduction is difficult. Furthermore, itis very difficult to downsize and reduce the thickness of the switchbecause optical beams are propagated in a three (3)-dimensional space.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalwavelength switch having a planar lightwave circuit structure capable ofsolving the above disadvantages and realizing reduction in the number ofassembly steps and in the cost.

In order to achieve the above object, according to a first aspect of thepresent invention there is provided an optical wavelength switch havinga planar lightwave circuit structure, comprising a first and a secondslab wave guides; an array wave guide connected with the first and thesecond slab wave guides; a movable mirror array having a plurality ofreflecting mirrors, arranged on the second slab wave guide opposite tothe side where the array wave guide is connected therewith; and anoptical wave guide arranged on the first slab wave guide opposite to theside where the array wave guide is connected therewith, for inputting aninput optical signal wavelength-multiplexed and outputting an opticalsignal wavelength-demultiplexed from the input optical signal, whereinthe optical wavelength switch has a focal point of an output opticalbeam from the second slab wave guide at the positions of the pluralityof reflecting mirrors constituting the movable mirror array, the opticalwavelength switch operable to switch the route of the optical signalreflectively inputted to the second slab waveguide, depending on the setdirection of reflection of the plurality of reflecting mirrors.

The plurality of reflecting mirrors constituting the movable mirrorarray may have dented reflecting faces, and the angle of reflection ofthe reflecting mirrors may be set by moving the dented reflecting facesalong a direction perpendicular to the optical axis.

Preferably, the optical wavelength switch includes a space between themovable mirror array and the second slab wave guide and includes at thedented portions a clad layer and a core layer having the same structureas that of the second slab wave guide.

In order to achieve the above object, according to a second aspect ofthe present invention there is provided an optical wavelength switchhaving a planar wave guide formed on a substrate, the planar wave guidehaving at least one wave-guide-type diffraction grating which includesan input/output wave guide, a first slab wave guide connected with theinput/output wave guide, an array wave guide whose one side is connectedwith the first slab wave guide, and a second slab wave guide with whichthe other side of the arraywave guide is connected, the opticalwavelength switch comprising a moving part supported in a cantileveredmanner on the substrate; and a reflecting mirror formed at the tip ofthe moving part such that it faces an end face of the second slab waveguide, wherein the reflecting mirror is obtained by forming a groovehaving a dented face on the moving part by etching such that the groovefaces the end face of the second slab wave guide, the reflecting mirrorbeing adapted to totally reflect at the dented face a optical beamoutputted from the end face of the second slab wave guide.

The moving part may have a clad layer having the same structure as thatof the slab wave guide. The core layer and the clad layer mayrespectively have a refractive index of 1.4142 or higher, with thegroove having the dented face forming an air layer. The relationshipbetween positions of the end face of the second slab wave guide and thedented face may be set such that the angle of incidence of a opticalbeam entering from the end face of the second slab wave guide into thedented face is 45 degrees or larger in an area from the dented face ofthe moving part toward the end face of the second slab wave guide.

In order to attain the above object, according to a third aspect of thepresent invention there is provided an optical wavelength switch havinga planar wave guide formed on a substrate, comprising a wave-guide-typediffraction grating which includes an input/output wave guide having anunder-clad layer on a sacrificial layer formed on the substrate, a corelayer formed on the under-clad layer and an over-clad layer formed onthe core layer, a first slab wave guide connected with the input/outputwave guide, an array wave guide whose one side is connected with thefirst slab wave guide, and a second slab wave guide with which the otherside of the array wave guide is connected; and a movable girder whoseone end is firmly secured to the substrate, the movable girder havingthe same under-clad layer, core layer and over-clad layer as those ofthe wave-guide-type diffraction grating, wherein the optical wavelengthswitch has a reflecting mirror at the tip of the movable girder, thereflecting mirror facing an end face of the second slab wave guide, withthe position of the reflecting mirror being set displaceable along adirection perpendicular to the optical axis.

Preferably, the face of the reflecting mirror toward the end face of thesecond slab wave guide is formed in a dented face.

The optical wavelength switch may have an air layer of a groove etchedto the sacrificial layer between the wave-guide-type diffraction gratingand the reflecting mirror. The reflecting face of the reflecting mirrormay be formed by forming a high-reflectivity film on a groove wall,toward the end face of the second slab wave guide, of the groove formedby etching reaching a part of the under-clad layer of the movable part.

It is preferred that the optical wavelength switch have two of thewave-guide-type diffraction grating. Preferably, the two first slab waveguides respectively have a part common to each other and are integratedsuch that end faces for connecting the input/output wave guide aredifferent from each other. Preferably, the two second slab wave guidesrespectively have a part common to each other and are integrated suchthat end faces for connecting respectively different reflecting mirrorarrays are different from each other.

In order to attain the above object, according to a fourth aspect of thepresent invention there is provided a method for fabricating an opticalfunction device having a wavelength switching function, the methodcomprising the steps of forming a sacrificial layer of GSG(germanium-added silica glass) on a silicon substrate: forming a waveguide structure having an under-clad layer and an over-clad layer ofBPSG (boron-and-phosphorus-added silica glass) or PSG (phosphorus-addedsilica glass) and a core layer of GPSG (germanium-and-phosphorus-addedsilica glass) formed between the under-clad layer and the over-cladlayer; forming the shape of a movable part and a wave guide end face byapplying anisotropic etching of the over-clad layer and the under-cladlayer or the core layer reaching the sacrificial layer; and separatingthe movable part from the substrate by removing the sacrificial layerbeneath the movable part by applying isotropic etching.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, aspects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram illustrating an ordinary optic add-drop module;

FIG. 2 is a diagram showing an example of a conventional composition ofa wavelength switch;

FIG. 3 is a diagram showing a composition of an optical wavelengthswitch having a planar lightwave circuit structure according to theinvention;

FIG. 4 is a diagram showing the operational principle of the invention;

FIG. 5 is a perspective view of an example of the composition of amovable mirror array 4 of an optical wavelength switch;

FIG. 6 is a plan view of the movable mirror array shown in FIG. 5;

FIG. 7 is a diagram showing the structure of the movable mirror array 4according to a second embodiment of the invention;

FIG. 8 is a diagram of the composition of an optical wavelength switchhaving another planar lightwave circuit structure according to theinvention and its operational principle is shown in FIG. 9;

FIG. 9 is a diagram showing the operational principle of the embodimentshown in FIG. 8; and

FIG. 10 is a diagram illustrating fabrication steps of a movable mirrorarray of an optical wavelength switch according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows a diagram of the composition of an optical wavelengthswitch having a planar lightwave circuit structure according to theinvention and FIG. 4 illustrates the operational principle of theinvention.

The planar optical wavelength switch structure according to theinvention shown in FIG. 3 is a PLC(Planar Lightwave Circuit) typecircuit formed on a silicon substrate using PLC technology and havingtwo (2) slab wave guides 1 and 3, an array wave guide 2 and a movablemirror array 4. An input wave guide 1A, output wave guides 1B and 1C areconnected with one side of the slab wave guide 1, and one side of thearray wave guide 2 is connected with the other side of the slab waveguide 1. The slab wave guide 3 is connected with the other side of thearray wave guide 2. Thereby, a wave-guide-type diffraction grating iscomposed.

Furthermore, on the PLC, the movable mirror array 4 integratedmonolithically is formed at a focusing position of the wave-guide-typediffraction grating.

The slab wave guides 1 and 3 are composed of planar mediums having a one(1)-layer or a multi-layer structure of dielectric etc. and has aproperty that it propagates optical signals in the direction along theplane. A multi-wavelength optical signal inputted into the slab waveguides 1 and 3 propagates spreading on a slab wave guide plane and thepropagated input optical beam 1A is inputted into an optical wave guideat the position corresponding to the array wave guide 2.

The optical signal propagated through the array wave guide 2 is suppliedwith a difference of an optical path length corresponding to the lengthof the array wave guide and is inputted into the slab wave guide 3. Theoptical signal propagates in a predetermined direction along a plane, isfocused by diffraction into a different direction for each wavelengthand is injected into the position of the movable mirror array 4.

FIG. 4 is a diagram illustrating the operational principle of themovable mirror array 4. In the figure, plurality of reflecting mirrorsare arranged corresponding to the focused position for each wavelength.Each of the reflecting mirrors forms a V-shaped reflecting mirror and isformed movable between a first state S1 and a second state S2 as shownin FIG. 4.

The path of a optical beam injected into a reflecting mirror moved tothe state S1 is turned by the reflecting mirror and the optical beam isinjected into the slab wave guide 3, being diverged to the rightcompared to the optical beam injected into the reflecting mirror.Therefore, the optical beam returns backward through the wave-guide-typediffraction grating and is focused at a position diverged from the inputwave guide. Therefore, the optical signal is outputted at the output 1Bby arranging the output wave guide at this focused position.

The optical beam reflected and returned by a reflecting mirror moved tothe state S2 similarly to the above, being diverged to the left comparedto the injected optical beam is outputted from the output wave guide 1C.

As described above, by switching the reflecting mirror to the state S1or the state S2 of the focused position of the optical beam for eachwavelength, an optical wavelength switch is composed, which switches anoptical beam inputted from the input port 1A such that it is outputtedfrom the output ports 1B or 1C for each wavelength.

In an example shown in FIG. 3, optical signals having respectivelywavelengths λ1-5 are wavelength-multiplexed as the input optical beam1A. The optical signals having the wavelengths λ2 and λ4 are outputtedat the first output port 1B and the optical signals having thewavelengths λ1, λ3 and λ5 are outputted at the second output port 1C.

FIGS. 5 and 6 show the composition of a first embodiment of the movablemirror array 4 constituting the optical wavelength switch of theinvention. FIG. 5 is a perspective view showing an example of thecomposition of the movable mirror array 4 of the optical wavelengthswitch. FIG. 6 is a plan view of the movable mirror array 4 shown inFIG. 5. Each of the figures shows only a part of a plurality of thereflecting mirrors constituting the movable mirror array 4.

In the movable mirror array 4 formed on a substrate 100 made of, forexample, silicon, a movable part consists of a movable part girder 40and a reflecting-mirror-forming part 41. The movable part does notcontact the substrate 100 and is supported above the substrate 100 by anend of the movable part girder 40 in a state like a cantilever.

In addition, movable part electrodes 40A and 40B are formed on both sidefaces of the movable part girder 40. The face of the end of thereflecting-mirror-forming part 41 on the side of the slab wave guide 3is V-shaped and a reflecting mirror 42 is formed on its surface by ametal film etc.

Furthermore, fixed parts 43 and 44 fixed to the substrate 100 are formednext to and respectively on both sides of the reflecting-mirror-formingpart 41, and fixed part electrodes 43A, 43B and 44A, 44B are formedrespectively on both sides of the fixed parts 43 and 44.

When a voltage is applied between the fixed part electrode 43A and themovable part electrode 40A, a static attraction force acts between bothof these parts, the movable part girder 40 fixed only at its one (1)side to the substrate 100 is attracted to the fixed part 43, the mirrorforming part 41 strikes a mirror positioning part 43C formed at the tipof the fixed part 43 and the state S1 is held.

Similarly to the above, when a voltage is applied between the fixed partelectrode 44A and a movable part electrode 40B, the state S2 is held.With such a structure, it is possible to switch an injected optical beamto the output 1 or the output 2.

As an embodiment of the invention, in the composition shown in FIGS. 5and 6, an electro-static force is used as the force to move a movablepart, however, the invention is not limited to this embodiment. Forexample, it is possible to obtain the same action as above using anelectromagnetic force, or using a force of a piezoelectric strain byforming a piezoelectric material on the side of a movable part.

In the embodiment of the invention, the switching function has beendescribed limiting the position of the reflecting mirror 42 to the stateS1 and state S2. However, it is possible to hold the reflecting mirrorat an intermediate state between the state S1 and the state S2 byadjusting the voltage to be applied between the electrodes.

In the case of such a structure, since the amount of optical beam to becoupled to an output can be adjusted, it is also possible for the switchto have a function as an optical variable attenuator.

When the difference between refractive indexes of the slab wave guide 3and air is large, the beam diameter of a optical beam emitted from theslab wave guide 3 becomes larger while the optical beam propagates thespace to the reflecting mirror 42. Thereby, coupling loss may becomelarge and reflection loss is generated at the end surface when theoptical beam is infected again into the slab wave guide 3.

In order to reduce this, it is possible to fill the space portion withmatching liquid having a refractive index equal to or somewhat higherthan that of the wave guide core layer.

FIG. 7 is a diagram showing the structure of the movable mirror array 4according to a second embodiment of the invention and FIG. 7A is a planview of a portion of the movable mirror array 4 and FIG. 7B shows across-sectional view formed by cutting out along the dotted line a-b inFIG. 7A. FIG. 7C is a plan view of a portion of the movable mirror array4 in the embodiment shown in FIG. 6 to be compared with FIG. 7A.

In FIG. 7, the composition except the reflecting-mirror-forming part 41is same as that of the first embodiment shown in FIGS. 5 and 6.

In the embodiment, for the reflecting-mirror-forming part 41, a mirrorpart slab wave guide structure 421 is formed inside the surface of thev-shaped reflecting mirror 42. This can be easily realized by forming amirror-forming groove 422 on the reflecting-mirror-forming part 41.

Thereby, it is possible to shorten a distance L1 for which the opticalbeam emitted from the slab wave guide 3 propagates free space (airlayer) until it is reflected by the surface of the reflecting mirror 4and is re-coupled to the slab wave guide 3 (the relationship between thedistance L1 and a distance L2 shown in FIG. 7C corresponding to theembodiment shown in FIG. 5 is L2>L1).

Thereby, according to the embodiment shown in FIGS. 7A and 7B, couplingloss of the movable mirror array 4 and the slab wave guide 3 can beconsiderably reduced.

Here, in the case where the angle of incidence from the slab wave guide3 to the slab wave guide structure 421 is set such that the requirementsfor total reflection at the V-shaped end face of the slab wave guidestructure 421 is satisfied, the V-shaped end face of the slab wave guidestructure 421 functions as it is as a total reflection mirror 42.Surely, it is possible that the end face can be used being coated with ahigh-reflectivity film such as a metal film.

In the embodiment, the angle of incidence of the optical beam emittedfrom the slab wave guide 421 to the V-shaped reflecting mirror 42 is setat 45° and the angle between the V-shape is formed such that its angleis 90°.

In the case where the wave guide core layer and the clad layer areformed such that their refraction index is 1.142 or more, therequirements for total reflection are satisfied between them and the airlayer in the groove part 422 when the optical beam emitted from the slabwave guide 3 enters into the slab wave guide 421. Thereby, the mirrorforming part end face functions as the total reflection mirror 42.

Furthermore, since the optical beam returned back at one (1) side of theV-shape enters the other side of the V-shape at the angle of incidenceof 45°, this point also can turn back the optical beam in parallel tothe emitted optical beam from the slab wave guide 3 toward the slab waveguide 3 satisfying the requirements for total reflection.

FIG. 8 is a diagram showing the composition of yet another opticalwavelength switch having a planar lightwave circuit structure accordingto the invention and FIG. 9 illustrates the operational principle ofthis embodiment.

In this embodiment, two (2) sets of the basic circuit of “a diffractiongrating + a mirror array” composed of the slab wave guides 1 and 3, thearray wave guide 2 and the movable mirror array 4 of the firstembodiment shown in FIG. 3 are prepared and they are composed such thatone of them is superposed on the other to share a part of slab waveguides 1 and 1′ and a part of slab wave guides 3 and 3′ respectively.

With such a composition, it is possible to reduce the footprint of thecircuit and to increase the number of chips obtained from one (1)silicon substrate. Furthermore, by coupling the outputs of the slabwaveguides 1 and 1′ of the two (2) basic circuits using couplers 50 and51, optical cross-connect function capable of exchanging optical beamshaving arbitrary wavelengths between inputs 1A and 1A′ and outputs 1Band 1C is possible.

For example, denoting wavelengths of optical signals of the input 1A and1A′ respectively as λA1-A5 and λB1-B5, optical signals having thewavelengths λA1, λB2, λA3, λB4 and λA5 are outputted as a first outputfrom the coupler 50 and optical signals having the wavelengths λB1, λA2,λB3, λA4 and λB5 are outputted as a second output from the coupler 51.

FIG. 9 is a diagram illustrating states of a plurality of reflectingmirrors in the movable mirror array 4 and 4′ to obtain the relationshipof inputs and outputs under such conditions. FIG. 9A is a diagramillustrating the states of the reflecting mirrors in the movable mirrorarray 4 corresponding to the slab wave guide 3. FIG. 9B is a diagramillustrating the states of the reflecting mirrors in the movable mirrorarray 4′ corresponding to the slab wave guide 3′.

Next, fabrication steps of a movable mirror array of an opticalwavelength switch according to the invention will be described referringto FIG. 10. FIG. 10A is a plane view of an optical wavelength switchhaving the structure of the reflecting-mirror-forming block 41 shown inFIG. 7A and the fabrication step will be described as follows takingthis as an example.

In FIG. 10B, a GSG (germanium-added silica glass) layer to be asacrificial layer 101 is first formed as a film on the silicon (Si)substrate 100, next, a BPSG (boron-and-phosphorus-added silica glass)layer or a PSG (phosphorus-added silica glass) layer to be an under-cladlayer 102 is formed and, then, a GPSG (germanium-and-phosphorus-addedsilica glass) layer to be a core layer 103 is formed as a film.

Next, an etching mask (photo-resist etc.) for forming a core pattern isformed on the core layer 102 and an isotropic etching is applied throughthis mask by RIE (Reactive Ion Etching).

A wave guide core pattern is fabricated by removing the core layer 103except the pattern portion. Thereafter, a BPSG layer to be an over-cladlayer 104 is formed as a film. Thereby, a core-embedded wave guidestructure is formed.

As methods for forming the films of sacrificial layer 101, theunder-clad layer 102, the core layer 103 and the over-clad layer,approaches such as CVD (Chemical Vapor Deposition), FHD (FlameHydrolysis Deposition), sputtering etc. may be used.

In FIG. 10C, an etching mask is formed on the over-clad layer withphoto-resist etc. and the portion down to the middle of the thickness ofthe under-clad layer 102 is etched by a directional etching such as RIE.Thereby, the mirror-forming groove 422 is formed as well as the sidefaces of the movable part girder 40 is exposed to the middle of thethickness of the under-clad layer 102.

Next, in FIG. 10D, a metal film is formed on the v-shaped end faceportion of the mirror-forming groove 422 and the side faces of themovable part girder 40 using CVD, electro-less plating, vapor depositionetc. Thereby, the reflecting mirror 42 and electrodes 40A and 40B areformed.

In FIG. 10E, furthermore, after the shape of the moving portion 40 hasbeen patterned with photo-resist etc., the shape of the moving part 40is formed by etching the silicon substrate 100 with a directionaletching such as RIE etc.

Finally, in FIG. 10F, after the portion other than the moving part 40has been masked with photo-resist etc., an etching is applied using avery dilute hydrofluoric-acid-and-nitric-acid solution (hydrofluoricacid:nitric acid:water=1:1:50).

In this step, a GSG (germanium-added silica glass) film being thesacrificial layer 101 is solved very fastbythehydrofluoric-acid-and-nitric-acid solution, by 100 times as fast asthe BPSG film or the PSG film forming the under-clad layer 102 and GPSGfilm forming the core. Therefore, it is possible to etch only thesacrificial layer 101 selectively. Thereby, the moving part 40 can beseparated from the substrate 100 and the moving mirror 4 in acantilever-girder shape can be formed.

Here, since the GSG layer is inserted for the selective etching, it isneedless to say that the GSG layer can be any kind of film as far as itis an insulating film having a larger etching selectivity ratio againstthe films forming the clad layer and the core layer.

In the above embodiment, at the moving mirror array 4, switching thereflecting mirror to either of the two (2) states S1 and S2 has beendescribed. However, it is possible to cause the reflecting mirror tohave a function as a variable attenuator by controlling it such that itis positioned at an intermediate position between the states S1 and S2as referred to previously.

Therefore, the definition of a term, “optical wavelength switch” in thisapplication covers an optical function device having a function as avariable attenuator.

As the embodiments have been described with reference to the drawings,according to the invention, an optical function device having awavelength switching function can be realized by using a wave-guide-typediffraction grating formed on a substrate with PLC (planar lightwaveCircuit) technology, for the spectral function and, furthermore,integrating MEMS mirrors on a substrate monolithically.

According to the invention, any alignment step is not necessary and thenumber of fabrication steps are considerably reduced since the spectralfunction part and the switching function part are integrated on one (1)substrate monolithically. In addition, drastic cost reduction can beexpected since batch fabrication is possible using wafer processes.

Furthermore, downsizing and thickness reduction can be easily realizedsince an optical beam is confined and propagated in a wave guidefabricated on a substrate. According to the invention, an opticalwavelength switch having a planar lightwave circuit structure isprovided that is capable of realizing reduction of the number of thefabrication steps and lower cost.

While illustrative and presently preferred embodiments of the presentinvention have been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

1. A method for fabricating an optical device comprising the steps of:forming a sacrificial layer of GSG (germanium-added silica glass) on asilicon substrate: forming a wave guide structure having an under-cladlayer and an over-clad layer of BPSG (boron-and-phosphorus-added silicaglass) or PSG (phosphorus-added silica glass) and a core layer of GPSG(gennanium-and-pbosphorus-added silica glass) formed between theunder-clad layer and the over-clad layer; forming the shape of a movablepart having a V-shaped end face, and a wave guide end face by applyinganisotropic etching of the over-clad layer and the under-clad layer orthe core layer reaching the sacrificial layer; forming metal films onthe V-shaped end face, and forming electrodes on both sides of themovable part; and separating the movable part from the substrate byremoving the sacrificial layer beneath the movable part by applyingisotropic etching.